Oscillating flow freezer

ABSTRACT

A freezer for a product includes a housing having a sidewall defining a chamber in the housing, and an inlet and an outlet in communication with the chamber; and a pair of pistons operatively associated with the housing and in communication with the chamber, the pair of pistons operable out of phase with each other for oscillating a gas flow within the chamber. A method is also provided for reducing a temperature of a product in a freezer.

BACKGROUND

The present embodiments relate to apparatus and methods for providing and controlling air flow and heat transfer effect across products in freezing systems.

Known freezers have a fan or a plurality of fans used to provide a convective airflow environment to accelerate the freezing rate of products, such as food products, being processed in the freezer. Fans require electrical energy to operate and contribute the thermal loads to the freezing processes which reduces the overall efficiency of the freezer.

The present inventive embodiments provide a freezer which eliminates the need for fans without reducing the effectiveness of the heat transfer effect upon the products.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present inventive embodiments, reference may be had to the following drawing figures taken in conjunction with the description of the embodiments, of which:

FIG. 1 shows a freezer in a first position constructed to provide an oscillating airflow and a method according to the present embodiments; and

FIG. 2 shows the embodiment of FIG. 1 in a second position.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a freezer apparatus is shown generally at 10 which is constructed to provide an oscillating flow of cryogenic gas to products to be chilled or frozen. The oscillating flow may in one embodiment operate repetitiously at high frequency. The cryogenic gas may be carbon dioxide (CO₂) or nitrogen (N₂), thereby permitting the apparatus 10 to be used with food products for example, as discussed below.

As used herein, “oscillating flow” refers to the flow of gas moving or traveling back and forth between two points regardless of the manner, number of repetitions or frequency of repetitions by which the oscillating flow is implemented.

The apparatus 10 includes a housing 12 in which a space 14 is provided for providing a chilling or freezing convective gas flow 16 to correspondingly chill or freeze products 18, such as food products, transported through the space 14 in the housing. The housing 12 also includes and inlet 20 and an outlet 22. An inlet skirt 24 or flap is provided at the inlet 20, while an outlet skirt or flap is provided at the outlet 22 to retain the gas flow 16 within the space 14. A transport apparatus 28, such as a conveyor belt for example, is disposed for operation to transport the products 18 from the inlet 20 through the space 14 to the outlet 22.

The space 14 is provided with a baffle 30 disposed beneath the conveyor belt 28. The baffle 30 may be of solid construction. An inlet exhaust flue 32 is disposed proximate the inlet 20 of the housing 12. An outlet exhaust flue 34 is disposed proximate the outlet 22 of the housing 12.

A pair of piston assemblies 36,38 are disposed at different sides of the housing 12. As shown in FIGS. 1 and 2, the assemblies 36,38 may be disposed at opposed sides of the housing 12. Each of the piston assemblies includes its respective piston 44,52. In one embodiment, the pistons 44,52 are operatively associated with the housing 12, as shown for example in FIGS. 1 and 2. A sidewall 40 and a sidewall 42 extend to form part of the housing 12. The sidewall 40 is formed to provide a cylinder for the piston 44, while the sidewall 42 is formed to provide a cylinder for the piston 52. The sidewalls 40,42 extend as shown in FIGS. 1 and 2 to connect to each other and form an upper baffle 31 at an interior of the space 14. The baffles 30,31 therefore coact to minimize a portion of the space 14 to provide a freezing chamber 15 for chilling or freezing within the space for the oscillating gas flow 16. This construction and arrangement provides for a more intense and effective gas flow across the product 18. The baffles 30,31 also prevent “dead space” above and below the baffles from interfering with and diluting the oscillating air flow 16. A vertical distance between the baffles 30,31 corresponds directly to the cross-sectional air flow area in the freezing chamber 72. A width of the conveyor belt 28 is therefore fixed. It is most efficient to operate the apparatus with a minimum acceptable height between the baffles 30,31. The height is therefore dependent upon a height of the product 18 being transported through the freezing chamber 72. When the cross-sectional area of the freezing chamber 72 is minimized, a velocity of the gas flow 16 on the surface of the product 18 can be increased with constant volumetric flow.

The sidewall 40 is constructed to provide a cylinder for the piston assembly 36 in which the piston 44 is disposed for reciprocating movement. The piston 44 is connected to a shaft 46 which can be of the screw jack or hydraulic type, which in turn is connected to a motor 48 for operating the piston. Seals 50 or gaskets mounted to the piston 44 prevent a majority if not all of the gas 16 from getting behind the pistons 44,52 into the respective cylinders. The sidewall 42 is constructed to provide a cylinder for the piston assembly 38 in which the piston 52 is disposed for reciprocating movement. The piston 52 is connected to a shaft 54 which can be of the screw jack or hydraulic type, which in turn is connected to a motor 56 for operating the piston. Seals 58 or gaskets mounted to the piston 52 prevent a majority if not all of the gas from getting behind the pistons into the respective cylinders.

As mentioned above, the sidewalls 40,42 are interconnected in the space 14 and therefore, for purposes of this disclosure, that portion of the sidewalls 40,42 in the space is referred to as the upper baffle 31.

The upper baffle 31 may be of solid construction and is provided with at least one hole 62 or port extending therethrough such that a pipe 64 or conduit can be inserted through the hole to introduce liquid cryogen into the freezer apparatus 10. The liquid cryogen provided, CO₂ or N₂, will usually phase change into a gaseous-solid phrase when injected into the chamber 15. The pipe 64 has a first end connected to a manifold 66 from which at least one or a plurality of nozzles 68 are in communication therewith. The manifold is disposed in the chamber 15. An opposite end of the pipe 64 is connected to a source of liquid cryogen (not shown). The pipe includes a control valve 70 for controlling an amount of the liquid cryogen to be introduced into the pipe and through to the manifold 66.

The baffles 30,31 coact to provide the freezing chamber 15 within the space 14. The cross section of the freezing chamber 15 is kept to as small a volume as possible in order to provide for increased velocity of a cryogen airflow 74 across the product 18, which in turn provides for increased heat transfer to the product.

A length of the housing 12 may be for example 3-20 meters and constructed as a tunnel freezer. The inlet and outlet skirts 24,26 can be constructed of rubber, plastic or stainless steel and are adjustable depending upon the dimensions of the product 18 entering and being discharged from the freezing chamber 15.

The sidewall 42 at the cylinder for the piston 52 is provided with a bleed gas pipe 76 or conduit which is in communication with an interior of the cylinder as shown in the Figures.

The apparatus functions as follows during operation. Referring to FIG. 1, the conveyor belt 28 transfers in this example food products 18 through the freezing chamber 15 the apparatus 10. The cryogenic injection assembly is arranged such that the manifold 66 will have at least one or alternatively a plurality of the nozzles 68 disposed more closely to the inlet 20 than to the outlet 22. The food product 18 being transported by the conveyor belt 28 is exposed to a cryogenic spray 72 as it passes in proximity to the nozzles 68. However, the oscillating gas flow 16 provides further heat transfer effect to the food products 18 as described below.

The pistons 44,52 work in unison, that is, the pistons will be at least approximately 180 degrees out of phase with each other, such that when the inlet piston 44 is moving in a downstroke, the discharge piston 62 is moving in an upstroke. Referring still to FIG. 1, as the piston 44 proceeds in the downstroke the airflow 74 is forced as a convective gas flow through and along the freezing chamber 15 as the gas flow is concurrently being drawn toward the piston 52 in the upstroke as represented by the arrows 78. As the piston 52 passes the bleed gas pipe 76, a select amount of the gas flow 78 is removed through the pipe 76 due to the flow actuating the swing check valve 83 to exhaust the flow from the chamber 15. It is also possible to synchronize the pistons 44,52 so that their respective strokes do not cause the piston 52 to move past the pipe 76, thereby providing for the continued reuse of the convective gas flow 16.

When the pistons 44,52 have finished their respective strokes as shown in FIG. 1, said pistons reverse direction as shown in FIG. 2. That is, for the next successive stroke shown in FIG. 2, the outlet piston 52 is forced downward to provide an airflow 80 back across the freezing chamber 15 toward the piston 36. Movement of the piston 52 in its downward stroke provides a venture effect where the bleed gas pipe 76 is in communication with the cylinder of the piston assembly 38, thereby moving the swing check valve 83 into the closed position, so as not to draw air or atmosphere external to the housing 12 into the freezing chamber 15. The airflow 80 is drawn by the upstroke of the inlet piston 44 as shown by the arrows 82. In addition, this return airflow 80 has the effect of recharging the airflow in the freezing chamber 15, because it is again subjected to the cryogen spray 69 being introduced into the freezing chamber by the nozzle(s) 68. Upon conclusion of the flow represented in FIG. 2, the pistons 36,38 again reverse direction and the cycle repeats itself as long as operationally necessary to chill or freeze the amount of products 18 to be processed.

A temperature gradient may also be provided by the apparatus 10 and the method employed by the apparatus. For example, from the inlet 20 to discharge at the outlet 22, a stroke length of the discharge piston 52 is increased thereby pulling more of the gas 78 in the direction of the outlet 22. The gas 78 can then be bled from the piston cylinder at the bleed gas pipe 76. A swing check valve 83 disposed in the bleed gas pipe 76 permits the gas to be bled from the piston cylinder and discharged as exhaust. A larger portion of the overall gas mass is therefore directed to the outlet 22 and therefore, the gas warms during the freezing process and the temperature gradient is established. The pistons 44,52 may be electronically controlled, and therefore a temperature gradient can be entered as an input to a control apparatus 84 connected to the pistons for operating the apparatus 10 at its most efficient setting. A desired temperature can be entered into the controller 84 by an operator. The control valve 70 is actuated to permit a desired flow of cryogen to the nozzles 68 to satisfy the temperature requirement for the product 18 and the freezing chamber 72. Control of the temperature gradient is not dependant upon a temperature set point. As described above, a delta T (ΔT) is entered into the controller 84 and same controls the mass flow of cryogen vapor along a length of the freezing chamber 72 to achieve the temperature gradient selected.

Another embodiment of the apparatus 10 includes moving the pistons 44,52 at shorter, quicker strokes along a distance of from approximately 2-6 mm. The frequency of reversing the airflow 16 more quickly will create a vibratory action of the airflow to increase heat transfer to the products 18 without expending as much energy as moving the pistons 44,52 through their full strokes.

The apparatus 10 and method of the present inventive embodiments provides for increased efficiency for using cryogen to chill or freeze the products 18 because no energy from fans is necessary in the apparatus. The apparatus 10 being able to operate its specific temperature gradients will also contribute toward higher efficiencies. There are fewer moving parts and therefore less maintenance for the apparatus 10.

It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result. 

What is claimed is:
 1. A freezer for a product, comprising: a housing having a sidewall defining a chamber in the housing, and an inlet and an outlet in communication with the chamber; and a pair of pistons operatively associated with the housing and in communication with the chamber, the pair of pistons operable out of phase with each other for oscillating a gas flow within the chamber to contact the product.
 2. The freezer of claim 1, further comprising a cryogen injection apparatus having a first end in communication with the chamber and a second end in communication with a source of liquid cryogen.
 3. The freezer of claim 2, further comprising a transport apparatus extending from the inlet through the chamber to the outlet for moving the product through the freezer.
 4. The freezer of claim 2, wherein the cryogen injection apparatus comprises at least one nozzle connected to the first end of the cryogen injection apparatus for providing a cryogenic substance to the chamber.
 5. The freezer of claim 2, wherein the cryogen injection apparatus comprises a manifold connected to the first end, the manifold having at least one nozzle for providing a cryogenic substance to the chamber.
 6. The freezer of claim 1, further comprising a bleed gas exhaust pipe in communication with the chamber proximate one of the pair of pistons for controlling removal of a portion of the oscillating gas flow from the chamber and preventing atmosphere external to the freezer from entering the chamber.
 7. The freezer of claim 1, further comprising an inlet exhaust funnel positioned proximate the inlet, and an outlet exhaust funnel positioned proximate the outlet.
 8. The freezer of claim 1, further comprising an inlet door mounted to the housing at the inlet and operable for restricting atmosphere external to the housing from entering the chamber, and an outlet door mounted to the housing at the outlet and operable for restricting the atmosphere external to the housing from entering the chamber.
 9. The freezer of claim 2, further comprising a control apparatus in communication with the pair of pistons and the cryogen injection apparatus for controlling upstrokes and downstrokes of the pair of pistons and injection of a cryogenic substance into the chamber.
 10. The apparatus of claim 2, wherein the liquid cryogen is selected from the group consisting of carbon dioxide and nitrogen.
 11. A method for reducing a temperature of a product in a freezer, comprising: providing a product to a chamber of the freezer for reducing a temperature of the product; injecting a cryogen substance into the chamber; oscillating an air flow within the chamber to charge the air flow with the cryogen substance; and contacting the product with the oscillating air flow.
 12. The method of claim 11, wherein the oscillating an air flow comprises operating a pair of pistons out of phase and in communication with the chamber for providing the oscillating air flow.
 13. The method of claim 12, wherein the operating comprises operating strokes of each one of the pair of pistons out of phase with other strokes of the other one of said pair, and each of said strokes extending along a distance of from 2 to 6 mm.
 14. The method of claim 11, further comprising: removing a portion of the oscillating air flow from the chamber; and establishing a temperature gradient across the chamber during the removing.
 15. The method of claim 14, further comprising controlling the injecting a cryogen substance, the oscillating an air flow and the removing a portion of the oscillating air flow to provide the temperature gradient across the chamber. 